This invention relates to method and apparatus for testing a DC motor and particularly relates to the testing of a permanent magnet DC motor. The following references were found in a search of the prior art: U.S. Pat. Nos. 2,890,410 to Holcomb; 3,061,777 to Bendell; 3,177,347 to Cowley; 3,651,402 to Leffmann; 3,758,857 to Simpson et al; and the publication "Measurement of Motor Time Constant," IBM Technical Disclosure Bulletin, Volume 14, No. 6, Nov., 1971 by W. L. Lohmeier.
Although the method and apparatus of the invention is believed to be generally suitable for testing other DC motors types, it is particularly suitable for the testing of DC motors of the permanent magnet type. Permanent magnet DC motors conventionally are tested with a dynamometer.
In the high volume production testing of permanent magnet DC motors with a dynamometer, a fixture is required to hold the motor securely in place and to maintain it in precise alignment with a torque coupler. The torque coupler connects the motor output shaft to a torque brake. The torque brake is used to apply a specified torque to the motor output shaft. Means must be provided for applying voltage to the motor terminals and for measuring such voltage. An electronic counter is required to measure and indicate the motor rpm. An ammeter also is required to indicate the current flowing in the motor under test. Typically, these components are located in a cabinet structure and each motor to be tested is placed in its best fixture and connected to the torque coupler. The motor terminals are electrically connected to the cabinet power supply, which applies a specific voltage across the motor terminals. A specific torque is applied to the output shaft of the motor in the direction opposite to normal motor rotation. The maximum current flow through the motor is recorded, as is the rpm of the output shaft. If the amperage and rpm are within specification limits established for the motor under test, the motor is considered acceptable and the test is complete. A complete dyamometer test cycle on a high volume production basis requires from 10 to 12 seconds for completion.